I grew up as a music student and loved going to the symphony as a kid, so I'm not necessarily the target audience here. But the one thing I notice when I go these days is that sitting through an entire performance challenges my attention span much, much more than it used to.
It's a common theme I've seen around HN, particularly with reading. The symphony isn't really a visual experience (unless they're showing video, which is becoming more common), and it can be really difficult to sit through sometimes, especially if you don't love the music. There are a couple of symphonies I love to listen to all the way, but most have a few exciting themes with several minutes of "meh" in between them IMO.